[PATCH] Disable Anonymous ECDH ciphersuites by default

[Maxim Dounin]

Hello!

On Tue, Jun 14, 2011 at 09:58:21AM +0100, Rob Stradling wrote:

> Hi.  NGX_DEFAULT_CIPHERS specifies !ADH to exclude the Anonymous DH 
> ciphersuites.  With OpenSSL-0.x, this has the effect of disabling all 
> ciphersuites that offer no authentication.  However, OpenSSL-1.x adds support 
> for Anonymous ECDH ciphersuites, and these are not disabled by !ADH.
> 
> !aNULL is the appropriate cipher string for disabling all anonymous 
> ciphersuites.  [1] observes that anonymous ciphersuites 'are vulnerable to a 
> "man in the middle'' attack and so their use is normally discouraged.'
> 
> Trivial patch attached.

Yes, thank you for the patch.  While not strictly necessary right 
now as nginx doesn't set ephemeral ECDH key and hence ECDH doesn't 
work anyway, I agree that using !aNULL is better.

> Apache httpd just committed a patch for the same issue [2].
> 
> [1] http://www.openssl.org/docs/apps/ciphers.html
> [2] https://issues.apache.org/bugzilla/show_bug.cgi?id=51363
> 
> Rob Stradling
> Senior Research & Development Scientist
> COMODO - Creating Trust Online

> diff -ur nginx-1.0.4/conf/nginx.conf nginx-1.0.4-defaultcipher/conf/nginx.conf
> --- nginx-1.0.4/conf/nginx.conf	2009-04-06 14:43:46.000000000 +0100
> +++ nginx-1.0.4-defaultcipher/conf/nginx.conf	2011-06-14 09:36:25.250146709 +0100
> @@ -106,7 +106,7 @@
>      #    ssl_session_timeout  5m;
>  
>      #    ssl_protocols  SSLv2 SSLv3 TLSv1;
> -    #    ssl_ciphers  ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP;
> +    #    ssl_ciphers  ALL:!aNULL:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP;
>      #    ssl_prefer_server_ciphers   on;
>  
>      #    location / {
> diff -ur nginx-1.0.4/src/http/modules/ngx_http_ssl_module.c nginx-1.0.4-defaultcipher/src/http/modules/ngx_http_ssl_module.c
> --- nginx-1.0.4/src/http/modules/ngx_http_ssl_module.c	2010-05-14 10:56:37.000000000 +0100
> +++ nginx-1.0.4-defaultcipher/src/http/modules/ngx_http_ssl_module.c	2011-06-14 09:33:42.085994902 +0100
> @@ -13,7 +13,7 @@
>      ngx_pool_t *pool, ngx_str_t *s);
>  
>  
> -#define NGX_DEFAULT_CIPHERS  "HIGH:!ADH:!MD5"
> +#define NGX_DEFAULT_CIPHERS  "HIGH:!aNULL:!MD5"
>  
>  
>  static ngx_int_t ngx_http_ssl_static_variable(ngx_http_request_t *r,

This should be changed in src/mail/ngx_mail_ssl_module.c as well.  
Otherwise looks good.  Tested just to be sure - works well here 
with OpenSSL 0.9.7 (oldest OpenSSL supported by nginx).

To Igor: could you please commit this (and the same change to 
mail)?

Maxim Dounin